Echelon Neuron C - Manual (Page 92)

80 How Devices Communicate Using Network Variables
// TODO: If needed by the application algorithm, transform
// the raw *pFloat NV value into the scaled float equivalent
// using the following formula:
// scaled = A * 10**B * (*pFloat + C)
// Scaling factors are accessible via the scaling_factor_X
// members of the SCPTnvType CP, for example
// nvo1::nvType.scaling_factor_a. This transformation is a
// costly operation and it is recommended to design
// the application algorithm such that this conversion
// is not required at all, if possible.
}
} // GetCurrent()
void SetCurrent(float_type* pFloat) {
// One union to hold all possible current types, plus the initial
// type of the changeable NV.
union {
unsigned long uLong;
signed long sLong;
SNVT_volt_f xInitial;
} nvLocal;
boolean
bConversionOK;
boolean bProcessABC;
bConversionOK = TRUE;
bProcessABC = nvoVolt::nvType.type_category == NVT_CAT_SIGNED_LONG
|| nvoVolt::nvType.type_category == NVT_CAT_UNSIGNED_LONG;
if (bProcessABC) {
// TODO: if needed by the application algorithm, revert the
// conversion done in GetCurrent() by using the following
// formula:
// raw = (*pFloat / (A * 10**B)) - C
// See GetCurrent(), above, for more details.
}
switch (nvoVolt::nvType.type_category) {
case NVT_CAT_SIGNED_LONG:
// Current type is signed long. Convert from float.
nvLocal.sLong = fl_to_slong(pFloat);
break;
case
NVT_CAT_UNSIGNED_LONG:
// Current type is unsigned long. Convert from float.
nvLocal.uLong = fl_to_ulong(pFloat);
break;
case NVT_CAT_INITIAL:
// Fall through to float.
case NVT_CAT_FLOAT:
// Float is current. No conversion is required, just
// copy data into local variable.
nvLocal.xInitial = *pFloat;
break;
default:
// Unsupported type. The changeLength() handler should
// have recognized this and rejected the type earlier.
// Log this application error and set the device offline:
error_log(TYPE_ERROR);
go_offline();
bConversionOK
= FALSE;
} // switch
if (bConversionOK) {
// Update the actual network variable in case the conversion
// was OK (current type is in fact supported).
// A more generic implementation of these conversion functions
// is likely to use a pointer to the changeable type network
// variable's initial type as a second argument, thus allowing
// the SetCurrent() and GetCurrent() functions to be used for
// all changeable type NVs of the same initial type.
// This approach is likely to require explicit calls to the
// propagate() function; see the Neuron C Reference Guide